This invention relates to automotive vehicle engine valves, and in particular to a bearing disposed within an exhaust gas recirculation (EGR) valve.
It is known in the art relating to automotive vehicle engines to provide selective recirculation of engine exhaust gases into the intake manifold in order to control exhaust emissions. To this end, an exhaust gas recirculation (EGR) valve may be provided which includes a valve assembly connectable with associated intake and exhaust manifolds or systems of the engine to meter the flow of exhaust gas from the intake to the exhaust.
EGR valves typically include a valve assembly operable to close or open a passage between the intake and exhaust manifolds. The valve assembly includes a valve member (or pintle) having a head connected with a shaft supported by a bearing for reciprocating motion within a valve body. An actuator assembly is operably connected with the valve assembly and includes a solenoid coil and an armature connectable with the valve member. The solenoid coil actuates the armature to open the EGR valve, which, in turn, is closed by a spring when the coil is deenergized.
To minimize leakage of exhaust gas into the valve assembly and/or the solenoid actuator, the diametral clearance between the valve shaft and its bearing is very tight, in the range of xc2x10.03 mm or less. The need to minimize gas leakage is balanced against the need to minimize hysteresis (and thus enhance actuator performance) which requires the diametral clearance between the valve shaft and its supporting bearing to be as large as possible (i.e. large enough to permit only an acceptable amount of exhaust gas leakage, less than 0.5 g/s, while limiting moisture intrusion).
In operation, the valve shaft is selectively exposed to exhaust gas as it operates to selectively admit exhaust gas into the valve assembly. Because exhaust gas (particularly diesel exhaust gas) has a high moisture content and is laden with particulates, the valve shaft may become coked, and the coking drawn into the bearing when the valve is closed. The accumulation of contaminants on the surfaces of the valve shaft and bearing may cause the shaft to seize in the bearing.
It is therefore desirable to provide a bearing having coking-resistant features that may be retrofit to any valve assembly, and in particular to EGR valves.
The present invention provides a coking-resistant bearing for use in an engine valve including a valve body defining an internal passage for the passage of exhaust gas through the valve and a valve member movable in the valve body for controlling exhaust gas flow through the passage, the valve member includes a shaft supported for reciprocating motion within the bearing.
The coking-resistant bearing includes an engagement surface having an end portion adjacent to the internal passage defined by the valve body. The end portion of the engagement surface includes at least one groove disposed therein sufficient to create an air pocket that resists fluid intrusion into said bearing. The groove may also include a scraping edge formed along the bearing surface such that the scraping edge of the groove gently scrapes against the valve shaft as it reciprocates along the engagement surface to remove contaminants from the shaft without interfering with shaft actuation.
To further inhibit the formation of coking contaminants within the bearing, a highly lubricious insert may be provided within the engagement surface of the bearing adjacent its end portion. The insert may be used within a bearing with or without an end portion including a groove.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.